JPH05218602A - Thin flexible circuit laminate using epoxy as base - Google Patents

Abstract

PURPOSE: To obtain superior mechanical characteristics, thermal characteristic and electrical characteristics by forming a laminate comprising a single- or double-clad type thermostable web, wherein epoxide is impregnated. CONSTITUTION: Single- or double-clad flexible circuit material contains a web 18 of woven fiber or unwoven fiber having thermostability under the state, wherein epoxide is impregnated and the temperature exceeds 260 deg.C. This web 18 is stuck to a conductive sheet 14. This flexible circuit laminate 10 has fire- resistant property and comprises a thermostable material that can be soldered. About 20-45wt.% of the web 18 is contained, with respect to a flexible substrate 12. The thickness of the substrate is 2-6 mils. The glass transition temperature of a dielectric material (polymer matrix for impregnation of the web 18) covers a wide temperature range of 20-50 deg.C. Thus, superior mechanical characteristics, thermal characteristic and electric characteristics can be obtained.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates generally to flexible circuit materials used in the manufacture of flexible electronic printed circuits. The invention is particularly directed to thin (2-6 mil) flexible circuit materials formed from laminates of single or double clad heat stable webs impregnated with epoxy.

[0002]

Flexible circuits are well known and are used in a myriad of electronic components that require interconnection of static or dynamic circuits. Minimal bending operation (minimum movement) when a flexible circuit must be bent to manufacture the circuit in a roll-to-roll process, when the circuit must be bent to install in a non-planar configuration, or when the circuit is applied
Static flex circuits are used when they need to be removed or re-installed only a few times during their useful life. Dynamic flex circuits are used when the flexible circuit undergoes continuous motion and moves significantly during use. An example of a dynamic flexible circuit is
Circuitry used to interconnect the read / write heads of a disk drive with a disk drive logic unit. The flexible circuit usually consists of a flexible film of polyimide or polyester material (eg KAPTON polyimide or MYLAR polyester from DuPont), which may be formed by adhesive layers or by using known direct deposition techniques such as sputtering. A coated metal plate of a conductive material (for example, copper foil) is attached. Although polyimide-based flexible circuits are well suited for their intended purpose, they are relatively expensive, which may not be an effective price for some applications, especially those using static flexible circuits.
On the other hand, polyester-based flexible circuit materials are not thermally stable at high temperatures and are not suitable for soldering or reflow soldering operations.

Epoxy-based circuit materials are well known,
Rely on epoxy chemistry or other disciplines. These materials may be hard (eg FR-4) or soft. Further, such epoxy-based circuit materials are disclosed in US Pat. No. 4,997,702, Ro
Gers Corporation to Bend / fl
It may be a flexible (and shape-retaining) type such as that marketed under the trade name ex. The circuit material described in Japanese Patent No. 4,997,702 includes a reinforcing fiber substrate having one or both sides bonded to a conductive sheet. The substrate comprises a nonwoven web impregnated with a polyfunctional or monofunctional epoxy and an anhydride or diacid. The glass transition temperature of the epoxy resin / hardener component is about 10 to 60 ° C., especially about 20 to 60 ° C.
It is 30 ° C. The thickness of the substrate is 8-60 mils. The circuit laminate material described in the patent 4,997,702 is 20 to 70 for reducing the coefficient of thermal expansion CTE in the Z direction.
It may include a web of a weight percent of inorganic filler material and / or a blend of glass fibers and polymer fibers. This circuit laminate is unique in that it is flexible in the sense that it can be bent into the desired multiplanar shape.
However, in contrast to conventional flexible materials, this circuit laminate retains its shape after bending.

Unlike the flexible shape-retaining circuit material described in US Pat. No. 4,997,702, the invention disclosed herein is an epoxy-based flexible material that does not retain its shape when bent or deformed. Regarding circuit materials. Many examples of such epoxy-based flexible circuit materials are known. U.S. Pat. No. 4,035,694 to Barton et al., For example, is a metal-clad type with a substrate that includes a nonwoven web impregnated with a polymeric binder (eg, a blend of branched acid-terminated polyester and an epoxy compound). Regarding a dielectric sheet. Alder, US Pat. No. 4,087,300, likewise relates to a flexible circuit laminate using an epoxy resin and an isocyanate curing agent. Patent No. 4,3 by Yamaoka et al.
No. 53,954 relates to a flexible circuit board material made of an epoxy resin coated on a copper foil. Yamao
Ka et al. did not use a web or other reinforcing material for the substrate. U.S. Pat. No. 4,140,831 relates to a flexible circuit material consisting of a nonwoven web (made of organic fibers) impregnated with an epoxy resin using polyanhydride as a curing agent. U.S. Pat. No. 4,191,800 likewise consists of an epoxy resin impregnated with a cross mat,
The present invention relates to a flexible circuit material having a metal coating on one side or both sides. U.S. Pat. No. 4,883,708 relates to a reinforced epoxy laminate circuit in which the epoxy resin comprises epoxy / carboxyl terminated nitrile or butadiene (CTBN) and the reinforcement is at least two types of fiber (glass fiber and polymer. (Including fibers). U.S. Pat. No. 4,913,955 likewise has an epoxy-based circuit characterized in that the epoxy component is an epoxy / CTBN resin and the reinforcement consists of a central glass woven layer and non-woven fibers on both sides. Regarding laminates. US Patent No. 4,8
No. 82,216 is an epoxy resin and polyhyal (pol).
Yield) compound and amine to form a matrix.

[0005]

Compared to polyimide based flexible circuits, the epoxy based flexible circuit materials described above have the advantage of lower cost, especially in static flex circuits. Epoxy-based flexible circuits are also more heat stable than polyester film-based circuit materials. However,
Despite much known about epoxy-based flexible circuits, at least as good (or better) electro-physical as polyimide or polyester-based flex circuits as static flex circuits. There is a constant need for low cost, thermally stable and improved epoxy-based flex circuits that are characteristic.

[0006]

SUMMARY OF THE INVENTION The aforementioned and other drawbacks of the prior art are overcome or ameliorated by the novel epoxy-based flexible circuit laminate of the present invention. In accordance with the present invention, single and double clad flexible circuit materials include epoxy impregnated heat stable webs that are laminated to a conductive sheet. This flexible circuit laminate is flame retardant and consists of a solderable, heat stable material. The epoxy resin component includes a polyfunctional epoxy resin (for example, a polyfunctional glycidyl ether of phenol novolac resin) and a polyanhydride curing agent. The thickness of the substrate is 50
˜150 microns (2-6 mils) and the glass transition temperature Tg of the dielectric material is over a wide temperature range of 20-50 ° C. The material can be used as is in a variety of flexible printed circuit components. Reinforced webs (woven or non-woven) provide the mechanical strength of the dielectric material necessary for handling and mounting components on the circuit during circuit manufacture.

While the above-mentioned prior art describes numerous examples of epoxy-based flexible circuit laminates,
None of these prior art is believed to disclose the new combination of elements that characterizes the flexible circuit laminate of the present invention. That is, all of the conventional techniques have (a) (1) a high temperature (heat stable) woven or non-woven web made of glass fiber or high temperature polyester fiber, and (2) a wide Tg of 20 to 50 ° C. , A flexible substrate having a multifunctional epoxy / polyanhydride curing agent for web impregnation, (3) a total thickness of 2 to 6 mils, and (b) at least one conductive material laminated to the substrate. It does not disclose a thin flexible circuit laminate consisting of a conductive material (copper foil) layer.

As mentioned above, none of the prior art epoxy based flexible circuit laminates have all of the features described above. The present invention combines these features and has advantages over known epoxy-based and polyimide- or polyester-based flex circuits. An important advantage of the present invention is the low cost resulting from the ability to use continuous lamination techniques during manufacturing and the relatively low cost of the materials (eg resins and webs). Moreover, flexible circuit laminates have similar (or less costly) mechanical, thermal and electrical properties (at a lower cost) when compared to conventional polyimide or polyester film based flex circuits applied as static flex circuits. Have.

[0009]

The above and other features of the present invention will be understood by those skilled in the art upon reading the following detailed description with reference to the accompanying drawings.

First, FIG. 1 shows a thin flexible circuit laminate 10 of the present invention. The circuit laminate 10 has a single clad shape and includes a substrate 12 to which a sheet of conductive material 14 is attached.

FIG. 2 is the same as FIG. 1 except that it shows the double clad configuration of the present invention. Therefore, FIG.
Double clad laminate 10 'includes an additional conductive layer 16 laminated to the bottom side of substrate 12'. The circuit laminate 10 of FIG. 1 and the circuit laminate 10 ′ of FIG. 2 are preferably manufactured by a continuous laminating method. This method
A roll of conductive material (copper foil roll) is continuously laminated to a substrate 12 (comprising a web impregnated with epoxy and other components) and hot pressed to provide a finished roll of a very thin flexible circuit laminate. Consists of doing.

Substrate 12 comprises an epoxy / polyanhydride matrix that impregnates the fibrous web. The matrix system comprises a polyfunctional epoxy resin crosslinked with a polyanhydride to produce a flexible thermosetting polymer with a glass transition temperature Tg of 20-50 ° C. It is preferred that the epoxy resin comprises a triglycidyl ether of para-aminophenol, a polyfunctional glycidyl ether of a phenol novolac resin, a diglycidyl ether of tetrabromobisphenol A, and mixtures thereof. Polyanhydride curing agents include polyadipic anhydride (PADA), polyazelaic anhydride (PAPA), and polysebacic anhydride (PSPA).
And dodecenyl succinic anhydride or mixtures thereof. Azelaic acid may be used in combination with any of the polyanhydrides mentioned above. This particular combination of epoxy resin and polyanhydride hardener broadens the Tg range to 20-50 ° C. The epoxy resin component is present in an amount of 40-70% by weight, based on the polymer matrix. The polyanhydride curing agent component is present in an amount of 60-30% by weight, based on the polymer matrix. These amounts can vary with the chemical functionality of the chemical reaction components (ie epoxy resin and hardener). In the preferred embodiment, a brominated diluent (eg, dibromophenyl glycidyl ether) is used as the epoxy modifier. The prior art typically uses structural modifiers such as carboxyl-terminated nitriles or butadiene (CTBN), polyester diepoxide compounds or a combination of epoxies and ethylene-acrylic elastomers to give the materials the required flexibility. In this respect, this particular matrix differs from most other prior art flexible epoxy based systems.

Fiber reinforcement (18 in FIG. 1 and 1 in FIG. 2)
8 ') is glass fiber (E, S, D glass) or high temperature polyester fiber (Kode manufactured by Eastman Kodak)
l) a heat-stable woven or non-woven web. The fibrous web is present in an amount of about 20-45% by weight, based on the total flexible substrate. Such thermal stable fiber reinforcements (which have thermal stability above 260 ° C.) allow the flexible circuit laminates of the present invention to withstand high temperatures during processing, especially solder melting temperatures.
Furthermore, the use of glass or high temperature polyester web reinforcements results in dielectric substrates 12, 12 'with relatively high mechanical strength that is comparable to or better than dielectric films made of polyester or polyimide only. Be done.

Preferred examples of woven and / or non-woven glass fiber webs for use in the present invention are set forth in Table 1 below.

[0015]

[Table 1]

1: Compressed to about 6 mils during laminating.

Preferred examples of high temperature polyester nonwoven webs include Eastman Kodak Model 211 series, 6 denier fibers.

An important feature of the circuit laminate of the present invention relates to the relative thickness of the laminate. Due to the combined thickness of the epoxy resin / curing agent, the woven or non-woven web of high temperature fibers, and the laminated conductive layer, the flexible circuit material may exhibit the required physical, electrical and cost advantages. Thus, the thin flexible material of the present invention has a thickness of 2-6 mils or 50-150 microns.

The flame retardant compound used in the present invention is a compound of 5
It is a brominated organic compound containing an epoxy resin part of ˜50 wt% (preferably 20-30 wt%). The brominated filler can be solid or liquid. Decabromodiphenyl oxide, pentabromodiphenyl oxide bis (2,3, dibromopropyl ether) of tetrabromobisphenol A, monofunctional brominated glycidyl ether, brominated imide (eg ethylene bistetrabromophthalimide) and brominated difunctional Epoxy compounds are typical examples of this class of flame retardants. The flame retardant system is more effective if a synergistic antimony compound is also included as a filler. The amount of synergistic compound (eg, antimony trioxide or antimony pentoxide) should be determined such that the bromine: antimony molar ratio is from 1: 1 to 5: 1 (preferably 2: 1 to 3: 1). ..

Further zinc borate is preferably added to the substrate matrix in order to minimize or eliminate the afterburning effect as measured by the standard burn test. In addition, small amounts of suitable binders (eg silane (glycidyl-propyl-trimethoxy-silane)) may be used to strengthen the bond between the matrix and the reinforcing web.

Any suitable electrically conductive material (preferably in roll form so that the continuous laminating process can be carried out) may be used in accordance with the present invention. Normally conductive material is copper (1/2
.About.3 ounces) and 1/2 or 1 ounce copper foil is the preferred conductive material 14,14 ', 16.

The following non-limiting Examples 1-8 further illustrate the novel, epoxy-based thin flexible circuit laminates of the present invention. All examples included a catalyst / promoter to increase the reaction rate. However, such catalysts / promoters are not required for the production of the circuit material composites of this invention.

Example 1 165 g of polyadipic anhydride (PADA), 20
A mixture of 8 g of triglycidyl ether of para-aminophenol and 150 g of dibromophenylglycidyl ether was first blended. Once a homogeneous mixture was obtained, 75 g of decabromodiphenyl oxide and 1
30 g of antimony trioxide was added to the mixture of epoxy and anhydride and stirred.

A non-woven web of glass fiber (Freudenberg type T1) using two roll applicators.
790) was impregnated with the hot resin mixture to form a laminate. The impregnated web was then placed in stage B at 90 ° C and then laminated to 1 oz / sqft of electrodeposited copper. 1
Lamination was performed at 200 to 500 ° C. at 00 to 500 psi. The resulting composite contained 25% by weight glass fiber and had a thickness of about 4 mils.

Using the same method as Example 1, the following Examples 2-8 were carried out. 1 oz / sq ft of copper was laminated and the substrate thickness varied from 2 to 6 mils.

Example 2 Material parts by weight Polyazelaic anhydride (PAPA) 770 Polyfunctional glycidyl ether of phenol novolac resin (average functionality = 2.2) 800 Diglycidyl ether of tetrabromobisphenol A 300 Dibromophenylglycidyl ether 431 Antimony trioxide 333 Non-woven fabric of zinc borate 6 polyester (Model) 680 Example 3 Material parts by weight Azelaic acid 170 Polyfunctional glycidyl ether of phenol novolac resin (average functionality = 3.6) 360 Dibromophenylglycidyl ether 320 Trioxide Antimony 120 ethylene-bis-tetrabromophthalimide 33 glycidyl-propyl-trimethoxy-silane 4 zinc borate 2 glass fiber woven fabric (BGS1610) 441 Example 4 (good) Preferred Example) Material Parts by Weight PAPA 112 Polyfunctional glycidyl ether of phenol novolac resin (average functionality = 3.6) 166 Dibromophenyl glycidyl ether 62 Antimony trioxide 57 Ethylene-bis-tetrabromo-phthalimide 16 Glycidoxy-propyl- Trimethoxy-silane 2 Zinc borate 1 Non-woven fabric of glass fiber (Vilene) (EPM4025) 103 Example 5 Material parts by weight Polysebacic anhydride (PSPA) 206 Diglycidyl ether of bisphenol A 250 Dibromophenylglycidyl ether 110 Antimony trioxide 95 Decabromo polyfunctional Gurishijirue of diphenyl oxide 47 polyester nonwoven (Kodel) 303 example 6 material parts PAPA 209 coupled bisphenol units Le (average functionality = 8.0) 373 dibromophenyl glycidyl ether 117 decabromodiphenyl oxide 58 antimony trioxide 205 glycidylpropyltrimethoxysilane 4 woven reinforcement glass fiber (Clark-Schwebel1080) 240 Example 7 material parts Dodecenyl succinic anhydride 266 Polyfunctional glycidyl ether of phenol novolac resin (Average functionality = 3.6) 178 Antimony trioxide 80 Decabromodiphenyl oxide 35 Polyester nonwoven fabric (Kodel) 185 Example 8 Material parts by weight PAPA 123 Bromine -Functionalized diglycidyl ether of modified phenol novolac resin 372 p-t-butylphenyl glycidyl ether 80 ethylene-bis-tetrabromo-phthalimide 21 zinc borate 3 Antimony trioxide 55 Glass fiber nonwoven (BGF1610) 284 Although a preferred embodiment has been shown and described, various modifications may be made to the invention without departing from the scope of the invention. Therefore, the present invention is exemplary and not limiting.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a single clad flexible circuit of the present invention.

FIG. 2 is a cross-sectional view of a double clad flexible circuit of the present invention.

[Explanation of symbols]

 10, 10 'Circuit laminate 12, 12' Substrate 14, 14 ', 16 Conductive layer 18, 18' Fiber reinforcement

Claims (10)

[Claims] 1. A woven fabric comprising (a) (1) at least one material selected from the group consisting essentially of glass fibers and polymer fibers, and having thermal stability above about 260 ° C. A web of fibers or non-woven fibers and (2) a polymer matrix for web impregnation consisting essentially of a polyfunctional epoxy and a polyanhydride having a broad glass transition temperature of 20-50 ° C. 3) An epoxy-based flexible circuit laminate comprising a flexible substrate having a thickness of 2-6 mils and (b) at least one layer of conductive material laminated to the flexible substrate. 2. The polyfunctional anhydride is selected from the group consisting of polyadipic anhydride, polyazelaic anhydride, polysebacic anhydride and dodecenyl succinic anhydride. The circuit laminate described in. 3. The polyfunctional epoxy is composed of triglycidyl ether of para-aminophenol, polyfunctional glycidyl ether of phenol novolac resin, diglycidyl ether of tetrabromobisphenol A, diglycidyl ether of bisphenol A and bound bisphenol units. The circuit laminate according to claim 1, which is at least one polyfunctional epoxy resin selected from the group consisting of functional glycidyl ethers. 4. The polyfunctional epoxy comprises a triglycidyl ether of paraaminophenol, a polyfunctional glycidyl ether of a phenol novolac resin, a diglycidyl ether of tetrabromobisphenol A, a diglycidyl ether of bisphenol A and a bound bisphenol unit. The circuit laminate according to claim 2, wherein the circuit laminate is at least one polyfunctional epoxy resin selected from the group consisting of functional glycidyl ethers. 5. The flexible substrate is approximately 20 to 45.
Wt% web present, about 40-70 wt% polyfunctional epoxy present on polymer matrix, and about 60-30 wt% polyanhydride present on polymer matrix. The circuit laminate according to claim 1. 6. The circuit laminate of claim 1 including a silane additive that enhances the bond between the polymer matrix and the web. 7. The circuit laminate of claim 1 including a synergistic combination of antimony and a brominated compound for flame retardancy. 8. The circuit laminate of claim 1 including a brominated diluent. 9. The circuit laminate of claim 8 wherein the brominated diluent comprises dibromophenyl glycidyl ether. 10. The circuit laminate of claim 1 including zinc borate.